This invention relates generally to improvements in fuel cell fuel delivery arrangements for use in combustion tools, and more specifically to metering valves used with such fuel cells for delivering the appropriate amount of fuel for use by a combustion tool during the driving of fasteners. While the present application is focused on the use of fuel cells in combustion tools, it is contemplated that other applications in which fuel cells or other pressurized containers using stem valves are employed, such as, but not limited to cosmetics and pharmaceutical products.
As exemplified in Nikolich U.S. Pat. Nos. 4,403,722, 4,483,474, 4,522,162, and 5,115,944, all of which are incorporated by reference, it is known to use a dispenser such as a fuel cell to dispense a hydrocarbon fuel to a combustion tool, also known as a combustion gas-powered tool, such as, for example, a combustion gas-powered fastener-driving tool. Such fastener-driving tools and such fuel cells are available commercially from ITW-Paslode (a division of Illinois Tool Works, Inc.) of Vernon Hills, Ill., under its IMPULSE trademark. In particular, a fuel cell of this type is described in Nikolich U.S. Pat. No. 5,115,944, listed above.
One design criterion associated with the use of such fuel cells, which contain separate compartments of pressurized fuel and propellant, is the prevention of leakage of one or both of the above constituents. The objective is to prevent or minimize leakage after production and before use, also known as shelf life, and also during periods when the fuel cell is installed in the tool but the tool is stored or otherwise not in use. As with other aerosol containers, a certain amount of leakage occurs over time. However, in the environment of combustion powered fastener driving tools, there is a concern that gradual leakage over a prolonged shelf life may result in reduced performance of the fuel cell due to insufficient propellant and/or fuel. Accordingly, present manufacturer recommendations call for a 12-18 month maximum shelf life of such fuel cells to ensure that sufficient propellant and/or fuel remains for expected performance needs.
Another design criterion of such fuel cells is that only a desired amount of fuel should be emitted by the fuel cell for each combustion event. The amount of fuel should be carefully monitored to provide the desired combustion, yet in a fuel-efficient manner to prolong the working life of the fuel cell. Prior attempts to address this dosage factor have resulted in fuel metering valves located in the tool (U.S. Pat. No. 5,263,439) or attached to the fuel cell (U.S. Pat. No. 6,302,297), both of which are also incorporated by reference.
Regardless of the above-listed locations of such fuel metering valves, fuel leakage has remained a design consideration. In the case of internal tool fuel metering valves, an excessive number of seal locations inherently create multiple opportunities for leaks. In the case of external fuel cell metering valves, to facilitate disposability of the fuel cell and valve, inexpensive materials are used. However, the aggressive nature of the fuel constituents in some cases cause premature failure of the valve seals or the valve housing itself.
Another design consideration of such fuel cells is that when metering valves are attached to the fuel cell, there is some duplication of components, in that a first valve controls the flow of fuel from the cell, and a second valve controls a metered dose of fuel for delivery to the tool for a single combustion event. A related concern is that when such cell-mounted metering valves are shipped with the fuel cell in an inoperative position, the user must activate the cell by moving the valve into position. It is thus difficult for the end user to discover and/or prevent fuel leakage due to improper installation of, or internal defects in, the metering valve.
Yet another design factor of cell-mounted metering valves is that once the metering valve is operationally installed, the main cell stem valve is continually open. Thus, the nature of the seal formed by the main fuel cell valve stem seal changes from a face seal to a radial seal about the valve stem. In this position, the seal is relaxed and provides less effective sealing. As such, there is a greater potential for fuel leakage from the fuel cell.
Accordingly, there is a need for an improved combustion tool fuel cell valve arrangement which reduces the number of components, and accordingly the potential for fuel/propellant leaks. There is also a need for an improved combustion tool fuel cell construction which reduces the number of sealing locations and the periodic loading on the main fuel cell valve stem.